In the development of radio communication systems, such as mobile communication systems (like for example GSM (Global System for Mobile Communication), GPRS (General Packet Radio Service), UMTS (Universal Mobile Telecommunication System) or the like), efforts are made for an evolution of the radio access part thereof. In this regard, the evolution of radio access networks (like for example the GSM EDGE radio access network (GERAN) and the Universal Terrestrial Radio Access Network (UTRAN) or the like) is currently addressed. Such improved radio access networks are sometimes denoted as evolved radio access networks (like for example the Evolved Universal Terrestrial Radio Access Network (E-UTRAN)) or as being part of a long-term evolution (LTE) or LTE-Advanced. Although such denominations primarily stem from 3GPP (Third Generation Partnership Project) terminology, the usage thereof hereinafter does not limit the respective description to 3GPP technology, but generally refers to any kind of radio access evolution irrespective of the underlying system architecture. Another example for an applicable broadband access system may for example be IEEE 802.16 also known as WiMAX (Worldwide Interoperability for Microwave Access).
In the following, for the sake of intelligibility, LTE (Long-Term Evolution according to 3GPP terminology) or LTE-Advanced is taken as a non-limiting example for a broadband radio access network being applicable in the context of the present invention and its embodiments. However, it is to be noted that any kind of radio access network may likewise be applicable, as long as it exhibits comparable features and characteristics as described hereinafter.
In the development of cellular systems in general, and access networks in particular, relaying has been proposed as one concept. In relaying, a terminal or user equipment (UE) is not directly connected with an access node such as a radio base station (e.g. denoted as eNodeB or eNB) of a radio access network (RAN), but via a relay node (RN) which is connected to the access node. Relaying by way of relay nodes has been proposed as a concept for coverage extension in cellular systems. Apart from this main goal of coverage extension, introducing relay concepts can also help in providing high-bitrate coverage in high shadowing environments, reducing the average radio-transmission power at the a user equipment (thereby leading to long battery life), enhancing cell capacity and effective throughput, (e.g. increasing cell-edge capacity and balancing cell load), and enhancing overall performance and deployment cost of radio access networks.
FIG. 1 shows a schematic diagram of a typical deployment scenario of a relay-enhanced cellular system, such as e.g. a LTE or LTE-Advanced RAN with radio-relayed extensions, for which exemplary embodiments of the present invention are applicable. As shown in FIG. 1, UEs at disadvantaged positions such as a cell edge and/or high shadowing areas are connected to a so-called donor base station (DeNB) via a respective relay node RN. Generally, any one of the relay nodes may be stationary/fixed or mobile.
The coverage or service area of a relay node may be referred to as relay cell, and the coverage or service area of a donor base station may be referred to as donor cell. Accordingly, both the DeNB as well as the RNs may be regarded as access nodes or base stations of an access network, possibly as access nodes or base stations of different hierarchical level in terms of logical and/or structural network deployment.
In a relay-enhanced cellular system, a relay node acts as a user equipment (UE) from the point of view of its serving donor base station (DeNB) and as a base station (eNB) from the point of view of its served user equipment or terminal (UE) of an actual user. Accordingly, a relay node supports both UE and eNB functionality and, thus, incorporates both UE and eNB functions. In the following, the user equipment (UE) function of a relay node is denoted by RN-UE, and the base station (eNB) function of a relay node is denoted as RN-eNB. This is indicated e.g. in FIG. 2 below.
FIG. 2 shows a schematic diagram of a system architecture of a relay-enhanced cellular system, such as e.g. a LTE or LTE-Advanced RAN with radio-relayed extensions, for which exemplary embodiments of the present invention are applicable. As shown in FIG. 2, further network entities and/or functions are involved, such as a mobility management entity/function (MME) for the RN-UE function and the user terminal, a serving gateway (SGW) and a packet data network gateway (PGW) entity/function for the RN-UE function and the user terminal, as well as an optional relay gateway (GW) entity/function. While various alternative implementations are conceived (being indicated the blocks denoted as Alt. 1, Alt. 2 and Alt. 3), the implementation according to Alt. 2 is currently specified as standard.
The individual entities/functions are linked by specified interfaces indicated between respective blocks in FIG. 2. In particular, the (wireless) link between donor base station (DeNB) and relay node (RN) is referred to as Un link or relay link, and the (wireless) link between the relay node (RN) and the terminal or user equipment (UE) is referred to as Uu link or access link.
In the development of cellular systems in general, and access networks in particular, the concept of closed subscriber group (CSG) has been proposed. For example, in current 3GPP specifications, CSGs are applicable for home base stations (H(e)NBs) or femtocells as well as macro base stations ((e)NBs) or macrocells. A cell with a closed subscriber group (CSG), also referred to as CSG cell is only allowed to be accessed by a terminal or user equipment when this terminal or user equipment is a member of the CSG of that cell or, stated in other words, is a member of that cell. In this regard, the parameters csg-indication and csg-identity are defined as CSG-related parameters for handling and managing access of CSG cells. The parameter csg-indication indicates whether or not a cell is a CSG cell, and the parameter csg-identity defines the identity of the CSG within the cellular system the cell belongs to. When csg-indication is set to TRUE for a specific cell, the terminal or user equipment is only allowed to access this cell, if the csg-identity matches an entry in the CSG whitelist of the terminal or user equipment. That is, in the context of CSGs, a specific CSG-based access control for a terminal or user equipment is required and specified from both UE side and network side.
The concept of closed subscriber group is generally applicable to relay-enhanced cellular systems. In such case, any relay cell may be a CSG cell or not, and any donor cell may be a CSG cell or not. The CSG-related parameters of the individual cells may be transferred by being included in System Information Block 1 (SIB1) according to current specifications so as to be advertised between relay node and donor base station.
While current specifications of CSG-based access control are applicable for a relay node when acting as a user equipment towards the network side, problems arise regarding the base station function of a relay node. Moreover, additional problems arise when the relay node (i.e. its base station function) has a closed subscriber group itself. That is, with specifications of CSG-based access control, problems arise in the access control of a relay node, in particular when a CSG is introduced both at the relay node and the donor base station, the two CSGs potentially exhibiting different settings, such as CSG ID and/or access mode (wherein the access mode could e.g. be hybrid/closed/open).
The above-mentioned problems are explained hereinafter.
FIG. 3 shows a schematic diagram of an exemplary deployment scenario of a relay-enhanced cellular system where both DeNB and RN represent CSG cells with different settings.
As shown in FIG. 3, both the DeNB and the RN represent CSG cells but with different CSG identities. A conceivable scenario of such deployment situation may for example be in an office or enterprise environment, where the DeNB is deployed to provide coverage to the whole building, while the RN is implemented in each floor or department to serve the staff on the specific floor or of the specific department only.
As described before, the RN combines both UE function and eNB function. Given this special feature of a relay node, for the access control, it cannot be considered just as a normal UE, because it provides network service (as an eNB) to other normal UE(s). It has been agreed in 3GPP that the RN should indicate to the network that it is a RN, if it would act as a. RN instead of normal UE, and the network side would confirm the RN identity based on the subscription info of the RN.
In current specifications, there is no consideration of an introduction of CSGs into relay systems. Hence, the currently discussed RN access control mechanism does not consider any CSG factors. Therefore, the existing CSG-based access control mechanisms specified for normal UEs will face some problems when applied for relay nodes because it does not consider the feature of the eNB function of the relay node but only its UE function.
In case a RN attaches to the network as (RN-)UE, the access control is performed by the MME based on the subscribed CSG list of the (RN-)UE and the CSG settings (i.e. CSG ID and access mode) of the accessed cell, i.e. the DeNB cell. After the RN passed the access control as a UE, the network activates the Un link. After that time, the RN acts as a RN and provides networks service to other UEs. Because no additional considerations of the CSG settings of the RN (i.e. the RN-eNB) where done before, when the DeNB was performing access control to the RN, it is possible that the RN provides network service to other UEs permitted based on the RN's CSG settings but not permitted based on the DeNB's CSG settings, which is because of the difference between the CSG settings of the DeNB and RN cells. For example, the DeNB cell may be configured with a CSG, while the RN cell may be configured with an open CSG or hybrid CSG.
In view thereof, there do not exist any feasible mechanisms for properly and correctly handling access control of a relay node with a closed subscriber group, in particular in case of layered CSG cells where a CSG cell is part of a relay node that itself is in a CSG cell of a donor base station, the layered CSG cells potentially exhibiting difference CSG settings.
Accordingly, mechanisms are needed for access control of a relay node with a closed subscriber group, in particular in case of layered CSG cells where a CSG cell is part of a relay node that itself is in a CSG cell of a donor base station, the layered CSG cells potentially exhibiting difference CSG settings.